1. Field of the Invention
The present invention relates to an energy efficient high pressure pump system applicable to paper manufacture and other uses.
2. Description of the Related Art
High pressure fluid is useful in many industrial applications. For example, in the paper industry, water and other fluids are used to shower, clean and otherwise treat papermaking fabrics used to form and dry a continuous paper sheet. These fabrics accumulate contaminants from the process, which must be removed, in addition to other deterioration in properties, which result from the applications and environment in which they are used. For example, a press fabric may be required to pass through one or more high pressure nips which apply great compressive pressure. The nip pressure causes the fabric to compress and close, affecting such operational characteristics as permeability of the fabric to water flow. These characteristics are critical to fabric operation.
There are essentially two basic methods to apply fluid to fabrics to affect operational characteristics. Low pressure, relatively high volume fluid can be applied to essentially flush contaminants away and flood or almost flood void volumes of fabrics. Higher pressure, lower volume flow can be applied, usually in concentrated streams, to apply power to the fabric and thus remove contaminants and mechanically affect other characteristics. In this regard see for example U.S. Ser. No. 08/498,909 entitled "Apparatus and Method of Fabric Cleaning", filing date Jul. 6, 1995 which has been allowed and which is commonly assigned and whose disclosure is incorporated herein by reference.
Conventional pressures in papermaking seldom exceed 2,500 psi since the generation of high pressures (up to 5,000 psi) in incompressible fluids is expensive and requires apparatus of inherent limitations. The pumping of incompressible fluid may be accomplished in a large number of ways. Most conventional and efficient is a rotating vane pump. Such a pump generally depends on a rotary impeller imparting energy to a fluid via centrifugal force. These pumps are common, and exist in a myriad of forms. In conventional applications, they are typically limited, however, to pressures of much less than 1,000 psi. As applications vary there is usually slippage within the pump body, which generates heat. If the application flow is allowed to fall below a specific threshold, cavitation or media vaporization occurs. The conventional method employed to prevent the aforementioned situation from occurring is to insure sufficient flow through the pump cavity. This is accomplished with use of waste gates or combination recirculation and cooling loops.
In the case where higher pressures are desired, there are fewer alternatives. This usually involves a positive displacement apparatus. A positive displacement pump is most commonly a variation of a reciprocating piston and cylinder, the flow which is controlled by some sort of valving. Reciprocal machinery is however less attractive than rotary machinery because it is inherently more complicated and less reliable than the rotary type. More importantly the output of a reciprocal machine is cyclic. The cylinder alternately pumps or fills. Therefore, there are breaks in its output. This disadvantage can be overcome to a certain extent by using multiple cylinders, and by passing the pump output through flow accumulators, attenuators, dampers or, as commonly done, waste gate the excess pressure thereby removing the high pressure output portion of the flow.
In addition to uneven pressure and flow output, reciprocating pumps have another disadvantage. They have uneven power input proportional to their output. This causes excessive wear and tear on the apparatus, and is inefficient because the pump drive must be sized for the high torque required when the position of the pump connecting rod is at an angular displacement versus crankarm dimension during the compression stroke that would result in the highest required input shaft torque.
Moreover, if the demand of the application varies, complicated bypass, recirculation or waste gate systems must be used to keep the pump from "dead-heading." That is, if flow output is blocked when the pump is in operation, the pump will either break down by the increased pressure developed or stall. If stalling occurs, a conventional induction electric motor will burn out as it assimilates a locked rotor condition with full rated voltage and amperage applied. Typical hydraulic systems with fixed displacement pumps use a relief valve to control the maximum system pressure when under load. When the flow required by the application is less than that delivered by the pumping system, the excess flow is vented by use of a relief valve.
Therefore, the pump delivers full flow at full pressure regardless of the application. This is a prime example of how a large amount of power is wasted.
In this regard, certain prior art that attempts to address such problems in differing environments should be noted. U.S. Pat. No. 513,589 to Metz describes a gear-train for a bicycle wherein the driven wheel includes a circular sprocket driven through a chain by an elliptical sprocket of the crankshaft.
U.S. Pat. No. 1,906,801 to Mather describes a dyeing machine, which includes an intergearing of an elliptical winch and a circular winch by a chain drive to ensure uniform surface speeds of the winches.
U.S. Pat. No. 2,648,986 to Guyer describes a pump drive employing an eccentric hub for adjusting the position of the drive belt toward and away from the drive wheel. This adjustment provides for varying the speed of the pump by changing the level of the belt on the surface of the drive wheel. This adjustment also provides for using different sizes of belts.
U.S. Pat. No. 2,994,216 to Morton describes a laundry apparatus, which employs an elliptical sheave mounted eccentrically to the shaft of a basket and which rotates about the shaft at all times with the basket.
U.S. Pat. No. 3,064,487 to Warwick et al. describes an eccentrically adjustable pulley adapter on a motor base shaft to eccentrically shift a transfer pulley stud so that a desired tension in the belt can be obtained.
U.S. Pat. No. 3,190,149 to Gorfin describes a speed reduction drive mechanism for converting power at high speed and relatively low torque to low speed and relatively higher torque. An eccentric disk is rotated about a shaft axis, to drive a gear, which undergoes a combined oscillating and reciprocating motion. The gear then transmits power to a cylindrical drive element and hence to a pulley, which drives a drive belt.
U.S. Pat. No. 4,936,812 to Redmond describes a torque reactive tension mechanism wherein an eccentric gear set is used as a means for automatically adjusting for fluctuations in the center distance of a power transmission drive system.
U.S. Pat. No. 5,427,581 to McGrath et al. describes an independently steerable idler pulley wherein a non-concentric inner sleeve bushing is mounted within a pulley. As the bushing rotates about its axis, the skew angle is translated to the pulley, thereby maintaining a belt in its properly mounted position on the pulley during operation.
U.S. Pat. No. 5,540,627 to Miyata describes an auto-tensioner for applying tension to a transmission belt by a tension pulley and for damping reaction forces acting from the belt.